检索结果-内蒙古大学图书馆

Cost minimization of real-time mission for software systems with rejuvenation

RELIABILITY ENGINEERING & SYSTEM SAFETY 2020年 193卷 106593-000页

作者： Levitin, Gregory Xing, Liudong Xiang, Yanping Univ Elect Sci & Technol China Sch Comp Sci Collaborat Auton Comp Lab Chengdu Sichuan Peoples R China Israel Elect Corp Ltd POB 10 IL-31000 Haifa Israel Univ Elect Sci & Technol China Sch Mech & Elect Engn Chengdu Sichuan Peoples R China Univ Massachusetts Dartmouth MA 02747 USA

This paper considers the optimal rejuvenation policy problem for software systems performing real-time tasks. Due to software aging, the system performance deteriorates with time eventually leading to the system crash, which can be catastrophic for critical applications. To prevent the system crash or minimize its occurrence probability, software rejuvenation has been widely adopted for counteracting the software aging effect but at the cost of extra system overhead and downtime. We derive the optimal state-based rejuvenation policy minimizing the total expected mission cost for software aging systems subject to multiple performance degradation states. The solution encompasses an event transition-based numerical method that assesses the total expected mission cost of a real-time task, covering penalty cost from the mission failure, operation cost of running the mission software and the expected rejuvenation cost. The proposed cost evaluation model can accommodate arbitrary types of state transition time distributions. The suggested model also allows simultaneous evaluations of other system performance metrics including the probability of the successful task completion (i.e., mission reliability) and conditional expected mission completion time given a successful mission task. Examples are presented to demonstrate the proposed methodology and optimizations. Effects of different parameters on the rejuvenation optimization solution are also investigated.

关键词： Event transition Mission cost Mission reliability Optimization Real-time task Software aging Software rejuvenation numerical algorithm

来源：评论

学校读者我要写书评

暂无评论

Analysis of control for a free boundary problem of steady plaques in the artery

引用

APPLIED MATHEMATICS AND COMPUTATION 2018年 331卷 473-483页

作者： Miniak-Gorecka, Alicja Nowakowski, Andrzej Univ Lodz Lodz Poland

In the earlier paper of Friedman et al. a simplified model of plaque growth involving LDL and HDL cholesterols, macrophages and foam cells is considered and they satisfy a coupled system of PDEs with a free boundary. The paper adds some control function to that model, allowing the controlled growth of LDL, HDL and plaque. Next, the new dual dynamic programming approach for free boundary problem is developed to formulate sufficient optimality conditions for the optimal steering of drugs. Finally an approximate optimality and numerical calculations are presented. (C) 2018 Published by Elsevier Inc.

关键词： Atherosclerosis Optimal control numerical algorithm

来源：评论

学校读者我要写书评

暂无评论

Revisiting Kac's method: A Monte Carlo algorithm for solving the Telegrapher's equations

引用

MATHEMATICS AND COMPUTERS IN SIMULATION 2019年 156卷 178-193页

作者： Zhang, Bolong Yu, Wenjian Mascagni, Michael Tsinghua Univ Dept Comp Sci & Technol BNRist Beijing 100084 Peoples R China Florida State Univ Dept Comp Sci Tallahassee FL 32306 USA Florida State Univ Dept Math Tallahassee FL 32306 USA Florida State Univ Dept Sci Comp Tallahassee FL 32306 USA Florida State Univ Grad Program Mol Biophys Tallahassee FL 32306 USA

In this work, we use Kac's stochastic model to derive a Monte Carlo (MC) algorithm for the numerical solution of the telegrapher's equation. The major ideas are to use random values under exponential distribution to facilitate the calculation of the random time, and to accelerate the simulation for multiple points through recycling random time simulation. Compared with the MC method recently proposed by Acebron and Ribeiro, the Kac's model based method is able to handle two-dimensional (2-D) and higher-dimensional problems with unbounded domain, and 2-D bounded-domain problems with the homogeneous boundary condition. Moreover, it has an efficient algorithmic implementation. With numerical experiments, we have validated the accuracy and efficiency of the proposed algorithms, and their applicability to some 2-D telegrapher's equations. (C) 2018 International Association for Mathematics and Computers in Simulation (IMACS). Published by Elsevier B.V. All rights reserved.

关键词： Hyperbolic partial differential equation Kac's stochastic model Monte Carlo method numerical algorithm The telegrapher's equation

来源：评论

学校读者我要写书评

暂无评论

Effective and flexible analysis for propagation in time varying waveguides

引用

OPTICAL AND QUANTUM ELECTRONICS 2004年第1-3期36卷 133-144页

作者： Al-Jarro, A Sewell, P Benson, TM Nerukh, A Univ Nottingham Sch Elect & Elect Engn Ctr Optoelect Electromagnet Res Grp Nottingham NG9 2RD England

The equivalence between the propagation of dispersive modal fields in two-dimensional waveguides, and plane waves in a one-dimensional plasma is presented. Exploitation of this equivalence allows a time domain variant of the effective index approach to be used to model dispersive waveguides problems very efficiently. A time domain integral equation is developed for this important practical case and the stability of a computer algorithm based upon it is improved by means of both a semi-implicit formulation and the use of a modified space - time mesh.

关键词： dimensionality reduction numerical algorithm time domain analysis

来源：评论

学校读者我要写书评

暂无评论

Standby mode transfer schedule minimizing downtime of 1-out-of-N system with storage

引用

RELIABILITY ENGINEERING & SYSTEM SAFETY 2023年第1期237卷

作者： Levitin, Gregory Xing, Liudong Dai, Yuanshun Southwest Jiaotong Univ Sch Comp & Artificial Intelligence Chengdu Peoples R China NOGA Israel Independent Syst Operator Haifa Israel Univ Massachusetts Dartmouth MA 02747 USA

Mode transfers have attracted attention from the standby system community as they can effectively reduce system downtime. However, the existing models are not applicable to standby systems with product storage. This paper advances the state of the art by modeling mode transfers in 1-out-of-N standby systems with storage, which saves surplus products generated during the system operation and these products may subsequently be used to supply the system demand. When the system demand cannot be supplied by the operating element or from the storage, the downtime incurs. Moreover, the length of the downtime may be affected by the mode transfer schedule of different elements. Thus, it is significant to determine the optimal mode transfer schedule (MTS) minimizing the expected mission downtime (EMD). To solve this optimization problem, a new numerical algorithm is put forward to evaluate the EMD of the considered standby system under a given MTS. The genetic algorithm is then implemented to solve the proposed optimal MTS problem. A detailed case study of a power generation system with five generators and a storage is conducted to demonstrate the proposed model and methodology. Effects of several parameters and their interactions on the EMD and optimization solutions are also demonstrated.

关键词： Mission downtime Mode transfer schedule numerical algorithm Standby system Storage

来源：评论

学校读者我要写书评

暂无评论

Stability and finite strain of homogenized structures soft in shear: Sandwich or fiber composites, and layered bodies

引用

INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 2006年第6期43卷 1571-1593页

作者： Bazant, ZP Beghini, A Northwestern Univ Evanston IL 60208 USA

The stability theories energetically associated with different finite strain measures are equivalent if the tangential moduli are transformed as a function of the stress. However, for homogenized soft-in-shear composites, they can differ greatly if the material is in small-strain and constant elastic moduli measured in small-strain tests are used. Only one theory can then be correct. The preceding variational energy analysis showed that, for sandwich columns and elastomeric bearings, respectively, the correct theories are Engesser's and Haringx's, associated with Green's and Almansi's Lagrangian strain tensors, respectively. This analysis is reviewed, along with supporting experimental and numerical results, and is then extended to arbitrary multiaxially loaded homogenized soft-in-shear orthotropic composites. It is found that, to allow the use of constant shear modulus when the material is in small strain, the correct stability theory is associated with a general Doyle-Ericksen finite strain tensor of exponent m depending on the principal stress ratio. Further it is shown that the standard updated Lagrangian algorithm for finite element analysis, which is associated with Green's Lagrangian finite strain, can give grossly incorrect results for homogenized soft-in-shear structures and needs to be generalized for arbitrary finite strain measure to allow using constant shear modulus for critical loads at small strain. (c) 2005 Elsevier Ltd. All rights reserved.

关键词： stability finite strain buckling critical loads homogenization composites sandwich structures elastomeric bearings layered bodies finite element analysis numerical algorithm

来源：评论

学校读者我要写书评

暂无评论

Elliptical fibre dielectric waveguides: a transverse transmission line analysis

引用

IET OPTOELECTRONICS 2020年第1期14卷 1-9页

作者： Boucouvalas, Anthony C. Papageorgiou, Christos Georgantzos, Euripides Univ Peloponnese Dept Informat & Telecommun Arcadia 22100 Greece Natl Tech Univ Athens Dept Elect Engn Iroon Politech 9 Athens 16121 Greece

The authors present a new method for determining the optical properties of arbitrary refractive index elliptical core fibres. The method applies the elliptic cylindrical coordinate system to Maxwell's equations and appropriately, using Fourier Transforms, operated on an elliptical core optical fibre waveguide, derives a flexible algorithm, which can be used to determine the optical properties of elliptical fibre waveguides. By dividing the fibre into a series of uniform consecutive thin dielectric layers transversely across the elliptical cross section with suitable transforming functions representing voltage and current themselves based on the electromagnetic field components, leads to transverse transmission line equations. The resonance frequencies of the cascaded matrices determine the mode propagation constants. The analysis leads to a numerical algorithm for calculating the exact modes of propagation constants. The method is analytically exact and computationally accurate, leading to algorithmic implementation, without making use of Mathieu functions which are solutions for step index waveguide. The advantage of this work is also the fact that it can be applied to arbitrary refractive index profiles. They present results of modal $\bar b - V$b over bar -V diagrams for various fibre ellipticities and also apply this method to determine the birefringence of graded index profile fibres and mode cut-off frequencies.

关键词： Maxwell equations electromagnetic fields optical fibres gradient index optics dielectric waveguides birefringence refractive index uniform consecutive thin dielectric layers elliptical cross section suitable transforming functions transmission line equations mode propagation constants numerical algorithm algorithmic implementation step index waveguide arbitrary refractive index profiles fibre ellipticities graded index profile fibres elliptical fibre dielectric waveguides transverse transmission line analysis optical properties arbitrary refractive index elliptical core fibres elliptic cylindrical coordinate system Maxwell's equations Fourier Transforms elliptical core optical fibre waveguide flexible algorithm elliptical fibre waveguides

来源：评论

学校读者我要写书评

暂无评论

Microplane Model M7 for Plain Concrete. I: Formulation

引用

JOURNAL OF ENGINEERING MECHANICS 2013年第12期139卷 1714-1723页

作者： Caner, Ferhun C. Bazant, Zdenek P. Univ Politecn Cataluna Sch Ind Engn Inst Energy Technol Barcelona 08028 Spain Northwestern Univ Dept Civil & Environm Engn Evanston IL 60208 USA McCormick Inst Evanston IL 60208 USA Northwestern Univ Evanston IL 60208 USA

Mathematical modeling of the nonlinear triaxial behavior and damage of such a complex material as concrete has been a long-standing challenge in which progress has been made only in gradual increments. The goal of this study is a realistic and robust material model for explicit finite-element programs for concrete structures that computes the stress tensor from the given strain tensor and some history variables. The microplane models, which use a constitutive equation in a vectorial rather than tensorial form and are semimultiscale by virtue of capturing interactions among phenomena of different orientation, can serve this goal effectively. This paper presents a new concrete microplane model, M7, which achieves this goal much better than the previous versions M1-M6 developed at Northwestern University since 1985. The basic mathematical structure of M7 is logically correlated to thermodynamic potentials for the elastic regime, the tensile and compressive damage regimes, and the frictional slip regime. Given that the volumetric-deviatoric (V-D) split of strains is inevitable for distinguishing between compression failures at low and high confinement, the key idea is to apply the V-D split only to the microplane compressive stress-strain boundaries (or strain-dependent yield limits), the sum of which is compared with the total normal stress from the microplane constitutive relation. This avoids the use of the V-D split of the elastic strains and of the tensile stress-strain boundary, which caused various troubles in M3-M6 such as excessive lateral strains and stress locking in far postpeak uniaxial extension, poor representation of unloading and loading cycles, and inability to represent high dilatancy under postpeak compression in lower-strength concretes. Moreover, the differences between high hydrostatic compression and compressive uniaxial strain are accurately captured by considering the compressive volumetric boundary as dependent on the principal strain differen

关键词： Constitutive modeling Inelastic behavior Cracking damage Yield limits Softening Concrete numerical algorithm Thermodynamic potentials Unloading

来源：评论

学校读者我要写书评

暂无评论

Unified periodic boundary condition for homogenizing the thermo-mechanical properties of composites

引用

APPLIED MATHEMATICAL MODELLING 2023年第1期121卷 252-269页

作者： Tian, Wenlong Qi, Lehua Northwestern Polytech Univ Sch Mech Engn Xian 710072 Peoples R China

This work emphasizes on the Periodic Boundary Condition (PBC) utilized in the Finite El-ement Homogenization (FEH) method to numerically determine the Thermo-mechanical (T-M) properties of composites. The unified numerical implementation algorithms of the PBC used for accurately predicting the elastic properties, coefficients of thermal expan-sion and elasto-plastic behaviors of composites and available for representative volume elements with conformal and non-conformal surface meshes, respectively, are proposed and detailed. Regarding not only the thermo-elastic properties of composites, but also the elasto-plastic behaviors of composites under both simple uniaxial tensile, shear, uniaxial cycle loading paths and complex non-radial loading paths, the unified numerical imple-mentation algorithms are verified to accurately predict the T-M properties of composites, through comparison with the results of the analytical models, the DIGIMAT-FE method, the experimental test and the results from the literature. The unified numerical imple-mentation algorithms of the PBC can be extended to the predictions of other properties of various composites. This work provides a comprehensive insight into the PBC used for predicting the T-M properties of composites and benefits development of future FE codes implemented in commercial software packages.(c) 2023 Elsevier Inc. All rights reserved.

关键词： Composite materials Finite element homogenization numerical algorithm Periodic boundary condition Thermo -mechanical properties

来源：评论

学校读者我要写书评

暂无评论

On implementing the implicit discrete-time super-twisting observer on mechanical systems

引用

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL 2023年第13期33卷 7532-7562页

作者： Winkler, Alexander Grabmair, Gernot Reger, Johann Univ Appl Sci Upper Austria Control Engn Grp Wels Austria Tech Univ Ilmenau Control Engn Grp Ilmenau Germany Univ Appl Sci Upper Austria Control Engn Grp Stelzhamerstr 23 A-4600 Wels Austria

In this paper, an extension of an algorithm for the implicit discretization of a super-twisting sliding mode observer is presented. Implicit and explicit discretization algorithms for homogeneous differentiators, where no physical model information is considered, are investigated in literature. This article studies the behavior when considering models of a rather general class of nonlinear systems. The discrete equations of the super-twisting observer are reformulated as generalized equation and an algorithm for the step-by-step solution is given. The uniqueness of the derived algorithm is investigated with an equivalent variational inequality formulation which is derived for a class of nonlinear systems. Furthermore, a semi-implicit predictor-corrector discretization is presented which is an approximation method for the presented algorithms and allows an explicit implementation in practical applications. Accuracy properties under noise and sampling are given. The algorithm is applied on two mechanical example systems taken from practice.

关键词： implicit discrete-time implementation mechanical system numerical algorithm robust state estimation super-twisting algorithm

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：